Detecting clutch slippage to measure drive line torque for clutch control during power shifts
A method for controlling clutch pressures during power shifts involving detecting clutch slippage, utilizing individual pressure control. In the shift, the pressure in the off-going clutch is ramped down over a time interval, for instance, an interval of from about 0.10 seconds to about 0.15 seconds, while the ratio of input speed to output speed is determined at more frequent intervals, such as about 0.01 second intervals, such that torque can be determined as a function of the clutch slippage. The speed ratio is checked frequently, for instance, 10 to 15 times during the ramp down of clutch pressure, resulting in 10 to 15 measured torque levels, to allow more precise adjustment of pressure in the off-going clutch, as well as the on-coming clutch.
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This invention relates generally to methods and apparatus for controlling clutches during power shifts, and more particularly, to a method and system for clutch control utilizing detection of clutch slippage to measure drive line torque for determining the required or desired clutch pressure curve.
BACKGROUND ARTTo achieve a smooth power shift when more than one clutch is involved, the pressure versus time signature or profile curve for the clutches must be varied according to the torque transmitted by the transmission. Referenced in this regard Bulgrien U.S. Pat. No. 5,251,132, issued Oct. 5, 1993 to Ford New Holland, Inc., which discloses controlling clutch pressure based on output shaft speed. Essentially, according to that patent, one clutch is released, and pressure is adjusted in the corresponding on-coming clutch based on the rate at which the output speed drops. However, it has been found that controlling clutch pressure based on output shaft speed results in less than desirable levels of smoothness in shift. The output speed can also be allowed to drop too fast or too far for the control system to react and increase pressure in the on-coming clutch.
Thus, what is sought is a new method for measuring drive line torque for clutch control during power shifts which provides better reaction ability and smoother shifting.
SUMMARY OF THE INVENTIONAccording to the invention, a method for controlling clutch pressures during power shifts involving detecting clutch slippage, is disclosed. According to one preferred method of the invention, individual pressure control for each clutch is utilized, and the pressure in the off-going clutch is ramped down over a time interval, preferably an interval of from about 0.10 seconds to about 0.15 seconds, while the ratio of input speed to output speed is determined at more frequent intervals, such as about 0.01 second intervals, such that torque can be determined as a function of the clutch slippage. The speed ratio is checked frequently, for instance, 10 to 15 times during the ramp down of clutch pressure, resulting in 10 to 15 measured torque levels, to allow more precise adjustment of pressure in the off-going clutch, as well as the on-coming clutch, as desired or required to provide sought after shifting characteristics, such as smoothness.
Because clutch slippage is detected while the clutch still has substantial torque capacity, smoother shifts can be made.
Referring now to the drawings wherein aspects of a preferred method according to the invention are shown, in
Typically, for power/shifting between two gears, whether under load or not, a first one of the clutches, denoted here as the off-going clutch, is disengaged, and a second one of the clutches, denoted as the on-coming clutch, is engaged, to complete the shift. The shift is initiated by the operator or driver using input devices such as a driver-actuated shift control 22 which can be, for instance, a movable shift lever or the like, and a clutch pedal 24. The respective operating states of control 22 and pedal 24 are communicated to an electronic controller 26, which includes a processor and appropriate circuitry for controlling the clutches, via suitable conductive paths 28 which can include wires or the like. Controller 26 is also connected by conductive paths 28 to an input speed sensor 30 positioned and operable for sensing the rotational speed of input 14, and an output speed sensor 32 positioned and operable for sensing the rotational speed of output 18. Both sensors 30 and 32 are operable for sending signals representative the sensed speeds to controller 26 in the well known, conventional manner.
The duration of the disengagement of the off-going clutch and the duration of the engagement of the on-coming clutch and the relative timing thereof are factors in determining the characteristics of the shift, including smoothness. The disengagement of the off-going clutch and the engagement of the on-coming clutch are fluid controlled operations, that is, each of the clutches contains fluid. Essentially, the fluid pressure in the off-going clutch is decreased to disengage it, and the pressure in the on-coming clutch is increased to engage it. To effect smooth disengagement of the off-going clutch it is desirable to reduce the fluid pressure gradually or in steps. The fluid pressure in the on-coming clutch can be increased gradually or in steps to effect smoother engagement. The relationship of fluid pressure in a clutch verses time can be plotted, and this plot or curve represents a signature of the relationship. Often, it is desirable to vary one or more characteristics of one or both of these curves, to improve one or more characteristics of a shift, for instance, smoothness.
The present invention involves a method for controlling clutch pressures during power shifts to provide desired shift characteristics, based on or as a function of detected clutch slippage. Individual pressure control for each clutch is utilized, and the pressure in the off-going clutch is ramped down over a time interval, preferably an interval of from about 0.10 seconds to about 0.15 seconds, while the ratio of input speed to output speed is determined at more frequent intervals, such as about 0.01 second intervals, based on sensed speeds from sensors 30 and 32. It has been observed that torque can be determined as a function of the clutch slippage. Thus, by determining ratios of input speed to output speed, clutch slippage can be determined, and from that data, torque can be determined. According to the invention, the speed ratio is checked frequently, for instance, 10 to 15 times during the ramp down of clutch pressure, including at times close to initiation of the ramp down, resulting in 10 to 15 measured torque levels. Using this data, precise adjustment of pressure in the off-going clutch, as well as the on-coming clutch, can be made as desired or required to provide sought after shifting characteristics, particularly smoothness. Because clutch slippage is detected while the clutch still has substantial torque capacity, it has been found that smoother shifts can be made.
Referring also to
It will be understood that changes in the details, materials, steps, and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.
Claims
1. A method for controlling a clutch pressure during a power shift comprising the steps of:
- a.) changing a pressure in a first clutch over a predetermined first time interval while calculating a ratio of an input speed on an input side of the first clutch to an output speed on an output side of the clutch at predetermined second time intervals shorter than the first interval to determine whether the first clutch is slipping;
- b.) adjusting a rate of change of the pressure as a function of determined clutch slippage;
- c.) changing a pressure in a second clutch over the predetermined first time interval while calculating a ratio of an input speed on an input side of the second clutch to an output speed on an output side of the second clutch at predetermined second time intervals shorter than the first interval to determine whether the second clutch is slipping; and
- d.) adjusting a rate of change of the pressure in the second clutch as a function of the determined second clutch slippage.
2. The method of claim 1, wherein the first time interval is from about 0.1 to about 0.15 second, and the second time intervals are each from about 0.01 to about 0.015 seconds.
3. The method of claim 1, wherein the first clutch is an off-going clutch and the pressure therein is decreasing.
4. The method of claim 1, wherein the second clutch is an on-coming clutch and the pressure therein is increasing.
5. The method of claim 1, wherein a calculate ratio is compared with a theoretical ratio to determine clutch slippage.
6. The method of claim 1, wherein the first clutch is an off-going clutch and tho pressure therein is decreasing and the rate of decrease in the pressure therein is increased when clutch slippage is present.
7. The method of claim 1, wherein the second clutch is an on-coming clutch and the pressure therein is increasing and the rate of increase in the pressure therein is increased when clutch slippage is present.
8. The method of claim 1, wherein the first clutch is an off-going clutch and the pressure therein is decreased during the shift and the rate decrease is changed as a function of the determined first clutch slippage.
9. The method of claim 1, wherein the second clutch is an on-coming clutch and the pressure therein is increased during the shift and the rate of increase is changed as a function of the determined clutch slippage.
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5211079 | May 18, 1993 | Runde et al. |
5251132 | October 5, 1993 | Bulgrien |
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5950789 | September 14, 1999 | Hosseini |
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Type: Grant
Filed: Jun 23, 2003
Date of Patent: Apr 19, 2005
Patent Publication Number: 20040255654
Assignee: CNH America LLC (New Holland, PA)
Inventors: Garth H. Bulgrien (Ephrata, PA), Yanming Hou (Racine, WI)
Primary Examiner: Eric S. McCall
Attorney: Collin A. Webb
Application Number: 10/601,781